An engine of a motorcycle has been known which has a balancer device so as to reduce vibrations, which are to be generated in association with reciprocal movement of a piston and rotation of a crankshaft (for example, refer to Patent Document 1 or Patent Document 2). In a balancer device disclosed in Patent Document 1 and Patent Document 2, a pair of balancer shafts having weights is disposed to be opposite to each other with sandwiching a crankshaft in a front-rear direction. One end of the crankshaft is provided with drive gears for driving the balancer shafts, and the drive gears are meshed with driven gears provided for the respective balancer shafts. Thereby, the rotation of the crankshaft is transmitted to each of the balancer shafts, so that periodical rotation vibrations of the crankshaft are cancelled.
Patent Document 1: Japanese Patent Application Publication No. H02-113145A
Patent Document 2: Japanese Patent Application Publication No. 2014-95405A
However, according to the engine disclosed in Patent Document 1 and Patent Document 2, while one end of the crankshaft is provided with the drive gears for driving the balancer shafts, the other end of the crankshaft is provided with a primary drive gear for driving a countershaft. In this way, since the drive gears for driving the balancer shafts and the primary drive gear for driving the countershaft are separately provided, the engine is enlarged in a vehicle width direction. For example, when the crankshaft is provided with the drive gears corresponding to the number of the balancer shafts, the engine is further enlarged in the vehicle width direction by the drive gears, which causes a severer problem.